Transistor body control circuit and an integrated circuit

Abstract

An integrated circuit comprises a transistor body control circuit for controlling a body of a bidirectional power transistor. The transistor body control circuit comprises switches connected between a body terminal and a first current terminal, with a control terminal for controlling the current flowing through the switch. The control terminal of the switch is connected to alternating current, AC capacitive voltage divider. The AC capacitive voltage dividers are connected to the control terminals and arranged to control the switches to switch the voltage of the body terminal as a function of the voltage between the first current terminal and the second current terminal. The integrated circuit further comprises a bi-directional power transistor connected to the transistor body control circuit.

The invention claimed is: 
     
       1. A transistor body control circuit for controlling a body of a bidirectional power transistor, comprising:
 a first switch connectable between a body terminal and a first current terminal of the bidirectional power transistor, comprising a control terminal for controlling the current flowing through the first switch; 
 a second switch connectable between the body terminal and a second current terminal of the bidirectional power transistor, comprising a control terminal for controlling the current flowing through the second switch; 
 the control terminal of the first switch being connected to a first alternating current, AC capacitive voltage divider and the control terminal of the second switch being connected to a second AC capacitive voltage divider; said AC capacitive voltage dividers being connectable to the first control terminal and the second current terminal and arranged to control the first switch and the second switch to switch the voltage of the body terminal to the first current terminal or the second current terminal as a function of the voltage between the first current terminal and the second current terminal. 
 
     
     
       2. A circuit as claimed in  claim 1 , where the AC capacitive voltage dividers both comprise a series connection of a resistor connectable to a respective current terminal of the transistor and at least two capacitive elements in series, a node between said capacitive elements being connected to the control terminal. 
     
     
       3. A circuit as claimed in  claim 2 , wherein the at least one of the first or second AC capacitive voltage divider comprises a diode, a cathode of said diode being connected to said resistor and an anode of said diode being connected to said node. 
     
     
       4. A circuit as claimed in  claim 1 , wherein for at least one of the first or second AC capacitive voltage divider a capacitive part of the switch to which the divider is connected forms a capacitive element of said AC capacitive voltage divider connecting the control terminal and the respective current terminal. 
     
     
       5. A circuit as claimed in  claim 1 , further comprising clamp circuitry for clamping the control terminals relative to said body terminal to below the breakdown voltage of the control terminal. 
     
     
       6. A circuit as claimed in  claim 5 , wherein further comprising, for at least one of the first or second switch, a resistor between the control terminal and the body terminal. 
     
     
       7. An integrated circuit, comprising a bi-directional power transistor, the integrated circuit comprising:
 a transistor body control circuit for controlling a body of a bidirectional power transistor, the transistor body control circuit comprising: 
 a first switch connectable between a body terminal and a first current terminal of the bidirectional power transistor, comprising a control terminal for controlling the current flowing through the first switch; 
 a second switch connectable between the body terminal and a second current terminal of the bidirectional power transistor, comprising a control terminal for controlling the current flowing through the second switch; 
 the control terminal of the first switch being connected to a first alternating current, AC capacitive voltage divider and the control terminal of the second switch being connected to a second AC capacitive voltage divider; said AC capacitive voltage dividers being connectable to the first control terminal and the second current terminal and arranged to control the first switch and the second switch to switch the voltage of the body terminal to the first current terminal or the second current terminal as a function of the voltage between the first current terminal and the second current terminal; 
 the integrated circuit further comprising a bi-directional power transistor connected with a body to said body terminal, with said first current terminal to a drain terminal and with a second current terminal to a source terminal. 
 
     
     
       8. An integrated circuit as claimed in  claim 7 , wherein the bi-directional power transistor comprises:
 a substrate with a substrate top surface; 
 a layer stack extending over the substrate top surface, in which stack a first vertical trench and a second vertical trench are present, each of said vertical trenches extending in a vertical direction from a top layer of the stack towards the substrate; 
 an electrical path which can be selectively enabled or disabled to allow current to flow in a first direction or a second direction, opposite to the first direction, between the drain terminal and the source terminal, the electrical path comprising: 
 wherein the drain terminal is situated, in said vertical direction, below the source terminal and the source terminal being situated on or above the top layer; and the body extends laterally between the first and second vertical trenches and vertically between said drain terminal and said source terminal; 
 the electrical path comprising: the body, a first drift region extending, in said vertical direction, between the body and the drain terminal, and a second drift region extending, in said vertical direction, between the body and the source terminal. 
 
     
     
       9. The integrated circuit as claimed in  claim 8 , comprising a control die on which the transistor body control circuit is provided and a power die on which the bi-directional power transistor is provided. 
     
     
       10. The integrated circuit as claimed in  claim 7 , where the AC capacitive voltage dividers both comprise a series connection of a resistor connectable to a respective current terminal of the transistor and at least two capacitive elements in series, a node between said capacitive elements being connected to the control terminal. 
     
     
       11. The integrated circuit as claimed in  claim 10 , wherein at least one of the first or second AC capacitive voltage divider comprises a diode, a cathode of said diode being connected to said resistor and an anode of said diode being connected to said node. 
     
     
       12. The integrated circuit as claimed in  claim 7 , wherein for at least one of the first or second AC capacitive voltage divider a capacitive part of the switch to which the divider is connected forms a capacitive element of said AC capacitive voltage divider connecting the control terminal and the respective current terminal. 
     
     
       13. The integrated circuit as claimed in  claim 7 , further comprising clamp circuitry for clamping the control terminals relative to said body terminal to below the breakdown voltage of the control terminal. 
     
     
       14. The integrated circuit as claimed in  claim 13 , wherein further comprising, for at least one of the first or second switch, a resistor between the control terminal and the body terminal. 
     
     
       15. The integrated circuit as claimed in  claim 7 , wherein the bi-directional power transistor has a breakdown voltage of at least 25 V and the first or second switch has a breakdown voltage below 10 V. 
     
     
       16. The integrated circuit as claimed in  claim 7 , wherein the bi-directional power transistor has a breakdown voltage from the drain terminal to the source terminal of at least 40 V and in reverse direction from the source terminal to the drain terminal of at least 25 V. 
     
     
       17. The integrated circuit as claimed in  claim 16 , wherein the breakdown voltage from the drain terminal to the source terminal is higher than in the reverse direction. 
     
     
       18. The integrated circuit as claimed in  claim 7 , wherein the AC capacitive divider has a division ratio which varies depending on a polarity of the voltage across the AC capacitive divider. 
     
     
       19. A circuit as claimed in  claim 2 , wherein for at least one of the first or second AC capacitive voltage divider a capacitive part of the switch to which the divider is connected forms a capacitive element of said AC capacitive voltage divider connecting the control terminal and the respective current terminal. 
     
     
       20. A circuit as claimed in  claim 3 , wherein for at least one of the first or second AC capacitive voltage divider a capacitive part of the switch to which the divider is connected forms a capacitive element of said AC capacitive voltage divider connecting the control terminal and the respective current terminal.